In some communications systems the data to be transmitted is compressed so that the available bandwidth is used more efficiently. For example, the Moving Pictures Experts Group (MPEG) has promulgated several standards relating to the compression of moving images and digital data delivery systems. The first, known as MPEG-1 refers to ISO/IEC standards 11172 and is incorporated herein by reference. The second, known as MPEG-2, refers to ISO/IEC standards 13818 and is incorporated herein by reference. A compressed digital video system is described in the Advanced Television Systems Committee (ATSC) digital television standard document A/53, and is incorporated herein by reference.
The above-referenced standards describe data processing and manipulation techniques that are well suited to the compression and delivery of video, audio and other information using fixed or variable length digital communications systems. In particular, the above-referenced standards, and other xe2x80x9cMPEG-likexe2x80x9d standards and techniques, compress, illustratively, video information using intra-frame coding techniques (such as run-length coding, Huffman coding and the like) and inter-frame coding techniques (such as forward and backward predictive coding, motion compensation and the like). Specifically, in the case of video processing systems, MPEG and MPEG-like video processing systems are characterized by prediction-based compression encoding of video frames with or without intra-and/or inter-frame motion compensation encoding.
Within respect to still images (or single image frames), several well known standards are utilized to effect compression of image information. For example, the Joint Photographic Experts Group (JPEG) has promulgated a several standard relating to the compression of still images, most notably the IS 10918-1 (ITU-T T.81) standard, which is the first of a multi-part set of standards for still image compression.
In the context of digital video processing and digital image processing, information such as pixel intensity and pixel color depth of a digital image is encoded as a binary integer between 0 and 2nxe2x88x921. For example, film makers and television studios typically utilize video information having 10-bit pixel intensity and pixel color depth, which produces luminance and chrominance values of between zero and 1023. While the 10-bit dynamic range of the video information may be preserved on film and in the studio, the above-referenced standards (and communication systems adapted to those standards) typically utilize a dynamic range of only 8-bits. Thus, the quality of a film, video or other information source provided to an ultimate information consumer is degraded by dynamic range constraints of the information encoding methodologies and communication networks used to provide such information to a consumer.
Therefore, it is seen to be desirable to provide a method and apparatus to preserve the dynamic range of film, video and other forms of relatively high dynamic range information that are encoded and transported according to relatively low dynamic range techniques. Moreover, it is seen to be desirable to provide such dynamic range preservation while utilizing economies of scale inherent to these relatively low dynamic range techniques, such as the above-referenced MPEG-like standards and techniques.
The invention comprises a method and apparatus for preserving the dynamic range of a relatively high dynamic range information stream, illustratively a high resolution video signal, subjected to a relatively low dynamic range encoding and/or transport process(es). The invention subjects the relatively high dynamic range information stream to a segmentation and remapping process whereby each segment is remapped to the relatively low dynamic range appropriate to the encoding and/or 10 transport process(es) utilized. An auxiliary information stream includes segment and associated remapping information such that the initial, relatively high dynamic range information stream may be recovered in a post-encoding (i.e. decoding) or post-transport (i.e., receiving) process.
Specifically, a method for encoding an information frame according to the invention comprises the steps of: dividing the information frame into a plurality of information regions, at least one of the information regions comprising at least one information parameter having associated with it a plurality of intra-region values bounded by upper and lower value limits defining a dynamic range of the information parameter; determining, for each of the at least one information region, a respective maximal value and a minimal value of the at least one information parameter; remapping, for each of the at least one information regions and according to the respective determined maximal and minimal values, the respective plurality of intra-region values of the at least one information parameter; and encoding each information region.